Phosphorus-copper-antimony-tin brazing alloy

ABSTRACT

A phosphorus-copper based brazing alloy comprising by weight: 4.0% to 8.0% phosphorus; about 0.1% to about 8% tin; 0% to about 2% antimony; and the balance copper.  
     A process of using this alloy to produce a brazed joint with a raised shoulder and with little black oxide.

[0001] This is a continuation-in-part of co-pending U.S. patentapplication Ser. No. 10/027,090, filed Dec. 20, 2001, which is acontinuation-in-part of U.S. patent application Ser. No. 09/913,000,filed Jul. 25, 2001.

BACKGROUND OF THE INVENTION

[0002] This invention relates to novel brazing filler metalcompositions. Two families of alloys (phos-copper andphos-copper-silvers) are used to braze copper and its alloys. Silverbrazing alloys (composed primarily of silver, copper, zinc, tin, nickel,manganese, and cadmium) are used to braze ferrous and non-ferrous metalsand alloys. These brazing alloys are designed to work at lowtemperatures and to provide strong, ductile joints.

[0003] Researchers in the past have discovered that additions of otherelements, such as tin and antimony, to phos-copper andphos-copper-silver, and nickel, manganese and lithium to silver brazingalloys, have increased the properties of these two families in importantways, adding strength to some and changing melting temperatures inothers. For example, U.S. Pat. No. 5,066,456 discloses that the additionof tin and antimony up to six percent each to a phosphorus copper basedalloy lowers brazing temperatures.

[0004] Applicant has discovered that an alloy containing by weight: 6.0%to 7.0% phosphorus, about 2% to about 8% tin, about 0% to about 2%antimony; and the balance copper, produces a brazed joint with greatlyimproved and previously unexpected properties.

[0005] The first of such new and unexpected properties is that the alloyforms a large cap, or shoulder, during the brazing process, and does soat a temperature that has not been possible with phosphorus/copperbrazing alloys in the past without the addition of silver to thecomposition of the alloys. In fact, these new alloys will form a cap orshoulder similar to or superior to a silver-containing phos/copper alloyand will do so at slightly lower liquidus temperatures than thesilver-containing alloys. The liquidus temperatures of brazing alloysmore closely represent the most important characteristic of where thealloy flows (the working temperature).

[0006] Air conditioning coils, heat exchangers, water coolers and othercopper coils are manufactured by connecting copper tubing and fittingsby brazing with copper-phosphorus or copper-phosphorus-silver brazingalloys. These alloys produce strong, ductile brazes, but the industryhas long experienced a relatively high percentage of leaks afterbrazing. Most leaks are caught on the production floor during testingand are repaired. This double work of brazing and testing is verycostly. More damaging, very tiny leaks can evade factory testing and endup as warranty work in the field that is both expensive and damaging tothe company's brand image.

[0007] The phos/copper alloys now on the market all range within asolidus temperature of 1310° F. to a liquidus temperature of 1500° F.Alloys of even higher phosphorus content, up to 8%, are now in used toenhance productivity because of their lower operating temperature costconsiderations. The non-silver alloys in this group are the mostcommonly used in industry and contain 7.1% to 7.4% phosphorus, thebalance being copper. The fact that these alloys flow and join very wellis problematic in that they also flow very thinly. Torch and furnacebrazing is performed as rapidly as possible to achieve goodproductivity. While these alloys are quick to braze, they are difficultto observe for soundness. The entire 360° of the brazed joint must becarefully viewed by the operator, for it is here that a correction, ifneeded, should be made. These thin-flowing alloys produce only a verysmall cap, or shoulder, around the pipe at the fitting junction. Thealloys are thin-flowing in that they flow like a heavy coating of paint,instead of more thickly as in a putty used to seal a ⅛ crack).

[0008] Even a skilled brazer cannot tell 100% of the time that he has atotally leak-free connection by visually looking at his completed braze.In some places on a given braze connection, the brazing alloy can beseen to be in places as a shoulder between the two parts, while in otherplaces the alloy drops in the adjoining area (the capillary) withoutforming any noticeable shoulder. When viewing this closely, the operatorcan often see that the joint appears to be 100% sound, but he can't becertain of it.

[0009] Most air conditioning companies submerge the copper coil, whichcomprises perhaps 100 brazes, into a water tank, and air pressure isadded to this coil to determine if there are any leaks. The now-in-usephos/copper alloys, as described above, could be modified to form anadvantageous cap by lowering the phosphorus content significantly.However, doing so is not feasible as the liquidus temperatures rise to apoint of endangering the copper being brazed.

[0010] It is noteworthy that silver in the range of 6-15%, when added tothe phosphorus/copper alloys described above, lowers the solidustemperature to 1190° F., allows the phosphorus contents to be reduced asmuch as 1.5%, allows the alloy to flow in a much thicker manner, andeffects a noticeable cap or shoulder to the brazed area. The popular 15%silver-phos-copper alloy has the consistency of hot taffy when hotenough to braze, and easily forms a large cap or shoulder at the jointarea. This visible fillet is quickly seen by the operator and anyomission can be remedied. However, the addition of silver is quiteexpensive.

[0011] Another serious deterrent to being able to observe the quality ofcopper tubing brazed with phos-copper or phos-copper-silver brazingalloys is the formation of a black oxide that is formed on the actualbraze surface and on the adjacent copper pipe. Because the braze and thecopper pipe all turn black, it is difficult to closely inspect theactual braze.

SUMMARY OF THE INVENTION

[0012] A process of using a phosphorus/copper/antimony/tin brazing alloyto produce a brazed joint with a raised shoulder and with little blackoxide, comprising the steps of:

[0013] a) melting an alloy comprising by weight:

[0014] 1. about 4.0% to about 8.0% phosphorus;

[0015] 2. about 0.1% to about 8% tin;

[0016] 3. 0% to about 2% antimony; and

[0017] 4. the balance copper;

[0018] b) applying the melted alloy to a joint to be brazed;

[0019] c) allowing the melted alloy to cool; and

[0020] d) forming a raised shoulder of solidified alloy about the jointwithout the substantial production of black oxide.

[0021] A principal object and advantage of the present invention is thatit produces a substantial raised shoulder or cap about the brazed joint,which is a visible sign to the operator that the joint is sound.

[0022] Another principal object and advantage of the present inventionis that it produces a brazed joint without significant black oxide,which can obscure the operator's view of the soundness of the joint.

[0023] Another principal object and advantage of the present inventionis that the addition of silicon adds important benefits to phos-copper,phos-copper-silver, and silver brazing alloys. The melting range ofthese brazing filler metals can be reduced significantly, saving cost byreducing the use of expensive fuel gases and the time required of thebrazing process.

[0024] Silicon addition to these alloys also creates the advantage oflowering the surface tension when they are in the molten state. Thisallows the brazing alloys to better penetrate tightly fitting parts andto achieve fuller coverage of the surfaces to be brazed. For example,leaks in copper coils used in air conditioning systems are often causedby small voids within a braze, connecting with one another, to form apath wherein refrigerant gases escape.

[0025] Silicon additions also offer the advantage of changing the colorand texture of phos-copper and phos-copper-silver brazes from a dull,grainy, brown finish to a very smooth finish of bright silver color. Toachieve this color and texture change, these alloys require a tin orantimony content of not less than 0.1 % or greater than 10% individuallyor in combination.

[0026] Silicon addition also increases the average tensile strength ofphos-copper alloys.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a cooling curve plotting liquidus temperatures of a40%-silver brazing alloy against the weight percent of added silicon.

[0028]FIG. 2 is an elevational view of a brazed copper joint that hasbeen brazed with a phos-copper alloy of the prior art.

[0029]FIG. 3 is an elevational view of a brazed copper joint that hasbeen brazed with a phos-copper-15% silver alloy of the prior art.

[0030]FIG. 4 is an elevational view of a brazed copper joint that hasbeen brazed with an alloy of the present invention.

[0031]FIG. 5 is a chart showing the tensile strength of variousphos-copper alloys in the presence and absence of silicon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0032]FIG. 2 shows a copper joint J that has been brazed with aphos-copper alloy of the prior art. Note the absence of any substantialshoulder about the brazed joint.

[0033]FIG. 3 shows a copper joint J that has been brazed with aphos-copper-15% silver alloy of the prior art. Although the joint has asubstantial shoulder or cap S, there is also substantial black oxide Oabout the joint which obscures the operator's view of the soundness ofthe joint.

[0034]FIG. 4 shows a copper joint that has been brazed with an alloy ofthe present invention. A substantial cap or shoulder S is present, and,in addition, there is little or no black oxide present.

[0035] The alloy of the present invention preferably comprises: about4.0% to about 8.0% phosphorus; about 0.1% to about 8% tin; 0% to about2% antimony; and the balance copper.

[0036] Most preferably, the alloy comprises either 6.75% phosphorus andabout 2% tin; or 6.7% phosphorus and about 6% tin.

[0037] The solidus temperature of the alloy is about 1178° F. and theliquidus temperature is about 1247° F.

[0038] The alloy may also contain about 0.01% to about 3% by weightsilicon, the benefits of which are disclosed in U.S. patent applicationSer. No. 09/913,000, which is a parent to the present application.

[0039] Table I shows working examples of the change in liquidustemperature of various phosphorus-copper brazing alloys with theaddition of various amounts of silicon. All values are percents byweight. TABLE I Alloy % Cu % P % Si Liquidus ° F. 1 92.9 7.1 0.0 1477 292.8 7.1 0.1 1465 3 92.6 7.1 0.3 1448 4 92.4 7.1 0.5 1430 5 91.9 7.1 1.01395 6 91.2 7.1 1.7 1343

[0040] Applicant expects that the benefits of the addition of siliconwill also extend to other alloys having a composition of from 89.0% to94.0% copper, 5.0% to 10.0% phosphorus, and 0.01% to 3.0 % silicon.

[0041] The substantial reduction of required brazing temperatureseffects considerable savings of both fuel gases and cycle time ofbrazing operations. The lower brazing temperatures also lessen thedegree of annealing caused to parent copper and brass metals with thephos-copper alloys. Such annealing causes the metal to soften and tobecome very weak. Also, in some very hot brazing furnaces, slightmelting of the copper or brass base parts can occur.

[0042] Addition of silicon as in Table I also results in a brazing alloywith lowered surface tension when melted.

[0043] Addition of silicon as in Table I also results in smoothersurfaces after brazing.

[0044] As silicon is added, in the presence of tin (0.1% to 6.0%) and/orantimony (0.1% to 6.0%) a color change is also effected to a brightsilver color finish after brazing.

[0045]FIG. 5 shows that the addition of a small amount of silicon alsosignificantly increases the tensile strength of phos-copper alloys.

[0046] Table II illustrates working examples of liquidus temperatures oftwo phos-copper alloys containing silver, with and without silicon. Allvalues are percents by weight. TABLE II Alloy % Cu % P % Ag % SiLiquidus ° F. 1 87.9 6.1 6.0 0.0 1485 2 87.4 6.1 6.0 0.5 1438 3 80.0 5.015.0 0.0 1462 4 79.5 5.0 15.0 0.5 1416

[0047] Applicant expects that the benefits of the addition of siliconwill also extend to other alloys having a composition of 59% to 92%copper, 5.0% to 10.0% phosphorus, 0.1% to 18.0% silver, and 0.01% to3.0% silicon.

[0048] A significant reduction in brazing temperature is apparent inboth of the silver alloys containing silicon.

[0049] Addition of silicon as in Table II also results in a brazingalloy with lowered surface tension when melted.

[0050] Addition of silicon as in Table II also results in smoothersurfaces after brazing.

[0051] As silicon is added, in the presence of tin (0.1% to 6.0%) and/orantimony (0.1% to 6.0%), a color change is also effected to a brightsilver color finish after brazing.

[0052]FIG. 1 is a graph of liquidus temperatures of an alloy composed of2% tin, 30% copper, 28% zinc, and 40% silver with the addition ofvarious amounts of silicon.

[0053] Applicant expects that the benefits of the addition of siliconwill also extend to other alloys with compositions of 20.0% to 40.0%copper, 5.0% to 80.0% silver, 10.0%% to 30.0% cadmium, 0.10% to 4.0%manganese, 0.50% to 4.0% nickel, 1.0% to 30.0% zinc, 0.50% to 10.0% tin,and 0.05% to 3.0% silicon.

[0054] The plotted curve shows meaningful reductions in liquidustemperatures throughout the range of silicon. As silicon is added tothis alloy, a color change is also effected. Without silicon, the alloyhas a color of bright silvery yellow. At 0.5% silicon, the color is alighter yellow, becoming a very light bronze at 1.5% silicon. When thealloy is composed of 2.8% silicon, the color is very close to the colorof sterling silver. With variations in tin and silver content, variouschanges in color are effected with the addition of silicon to the silverbrazing alloy family. This has definite advantages in decorativeapplications such as jewelry and other arts.

[0055] Experiments have also shown that the addition of 0.01% to 3.0%silicon to soft solders lowers the surface tension of the solders,allowing better flow into tight connections and hardening the solders,adding strength and wear resistance. Silicon addition may also affectelectrical conductivity of the solder. Soft solders come in manydifferent alloys: lead-tin, tin-antimony, tin with copper or silver.Other metals used are zinc, aluminum, bismuth, nickel, cadmium, andindium.

[0056] An example of an alloy in common usage is composed of 6% Ag, 6.1% P, balance Cu. It has a solidus temperature of 1190° F., a liquidusof 1465° F., and is ductile. One embodiment of the present invention isof an alloy of 3% Ag, 2% Sn, 6.1% P, 0.1% Si, and the balance Cu. It hasa solidus temperature of 1109° F. and a liquidus temperature of 1477° F.This alloy is quite ductile, forms a large shoulder or cap, and has abright color when brazing is being performed. Brazing is accomplished ata lesser temperature, the braze is more visible to the operator toenable corrections, and the alloy is ductile enough to braze brassalloys that heretofore were brazed only with silver/phos/copper alloyscontaining from 6 to 15% silver.

[0057] The present invention may be embodied in other specific formswithout departing from the spirit or essential attributes thereof, andit is therefore desired that the present embodiment be considered in allrespects as illustrative and not restrictive, reference being made tothe appended claims rather than to the foregoing description to indicatethe scope of the invention.

What is claimed:
 1. A phosphorus-copper based alloy comprising byweight: a. about 4.0% to about 8.0% phosphorus; b. about 0.1% to about8% tin; c. 0% to about 2% antimony; and d. the balance copper whereinthe alloy produces a brazed joint with a substantial shoulder andwithout substantial black oxide.
 2. The phosphorus-copper based alloy ofclaim 1, wherein the percentage of phosphorus is 6.75%.
 3. Thephosphorus-copper based alloy of claim 1, wherein the percentage ofphosphorus is 6.7% and the percentage of tin is 6%.
 4. Thephosphorus-copper based alloy of claim 1, wherein the solidustemperature is about 1178° F. and the liquidus temperature is about1247° F.
 5. The phosphorus-copper based alloy of claim 1, furthercomprising by weight about 0.001% to about 3% silicon.
 6. Thephosphorus-copper based alloy of claim 1, further comprising about 0.1%to about 18% silver.
 7. A process of using aphosphorus/copper/antimony/tin brazing alloy to produce a brazed jointwith a raised shoulder and with little black oxide, comprising the stepsof: a) melting an alloy comprising by weight:
 1. about 4.0% to about8.0% phosphorus;
 2. about 0.1% to about 8% tin;
 3. 0% to about 2%antimony; and
 4. the balance copper; b) applying the melted alloy to ajoint to be brazed; c) allowing the melted alloy to cool; and forming araised shoulder of solidified alloy about the joint without thesubstantial production of black oxide.
 8. The process of claim 6,wherein the percentage of phosphorus is 6.75%.
 9. The process of claim6, wherein the percentage of phosphorus is 6.7% and the percentage oftin is 6%.
 10. The process of claim 6, wherein the solidus temperatureis about 1178° F. and the liquidus temperature is about 1247° F.
 11. Theprocess of claim 6, wherein the allow further comprises by weight about0.01% to about 3%% silicon.
 12. The process of claim 7, furthercomprising about 0.1% to about 18% silver.